Passive entry/passive start communication systems with selected antennas having multiple polarized axes

Abstract

A method of communicating with a portable access device includes iteratively performing an algorithm via an access module of a vehicle. The algorithm includes a series of operations including: selecting a frequency from multiple frequencies; selecting an antenna pair from multiple possible antenna pairs, where antennas of the possible antenna pairs include antennas with different polarized axes; transmitting a packet to the portable access device via the selected antenna pair; receiving a first RSSI and a response signal from the portable access device, the first RSSI corresponds to the transmission of the packet; and measuring a second RSSI of the response signal; based on the first RSSIs and the second RSSIs. A best one of the frequencies and a best antenna pair of the possible antenna pairs are selected. One or more additional packets are transmitted using the selected best frequency and the selected best antenna pair.

What is claimed is: 
     
       1. A method of communicating with a portable access device, the method comprising:
 iteratively performing an algorithm via an access module of a vehicle, wherein the algorithm includes a series of operations comprising
 selecting a frequency from a plurality of frequencies, 
 selecting an antenna pair from a plurality of possible antenna pairs, wherein antennas of the plurality of possible antenna pairs include antennas with different polarized axes, 
 transmitting a packet to the portable access device via the selected antenna pair, 
 receiving a first received signal strength indicator (RSSI) and a response signal from the portable access device, wherein the first RSSI corresponds to the transmission of the packet, and 
 measuring a second RSSI of the response signal; 
 
 obtaining the first RSSIs and the second RSSIs measured during iterative performance of the algorithm; 
 based on the first RSSIs and the second RSSIs, selecting (i) a best antenna pair of the plurality of possible antenna pairs with highest RSSI values out of the first RSSIs and the second RSSIs, and (ii) one of the plurality of frequencies, to provide a selected frequency and antenna pair combination; and 
 transmitting one or more additional packets using the selected frequency and antenna pair combination. 
 
     
     
       2. The method of  claim 1 , wherein each selected antenna pair includes a linear polarized antenna and a circular polarized antenna. 
     
     
       3. The method of  claim 1 , further comprising:
 transmitting the one or more additional packets to authorize the portable access device; 
 determining whether the portable access device is authorized to access an interior of the vehicle; and 
 permitting access to an interior of the vehicle if the portable access device is authorized. 
 
     
     
       4. The method of  claim 3 , further comprising:
 measuring time-of-flight of the one or more additional packets including time to transmit the one or more additional packets to the portable access device and time to receive one or more responses from the portable access device; and 
 based on the measured time-of-flight, estimating a distance between the vehicle and the portable access device. 
 
     
     
       5. The method of  claim 4 , wherein the estimated distance is used to detect whether another device is attempting to perform a range extender type relay station attack. 
     
     
       6. The method of  claim 5 , further comprising, if the another device is attempting to perform the range extender type relay station attack, performing a countermeasure including preventing access to the interior of the vehicle. 
     
     
       7. The method of  claim 6 , wherein the countermeasure includes notifying an owner of the vehicle of the range extender type relay station attack. 
     
     
       8. The method of  claim 3 , further comprising:
 exchanging multiple pairs of unmodulated carrier tones with the portable access device at multiple frequencies, wherein the pairs of unmodulated carrier tones include received tones and transmitted tones; 
 measuring phase of received tones relative to transmitted tones and gathering frequency data; and 
 estimating a distance between the vehicle and the portable access device based on the measured phases and frequency data. 
 
     
     
       9. The method of  claim 8 , further comprising determining whether another device is attempting to perform a range extender type relay station attack based on the estimated distance. 
     
     
       10. The method of  claim 1 , wherein the each selected antenna pair includes linear polarized antennas. 
     
     
       11. The method of  claim 1 , wherein the algorithm includes switching between the plurality of possible antenna pairs between consecutively transmitted packets. 
     
     
       12. The method of  claim 1 , wherein the algorithm includes switching between the plurality of possible antenna pairs during transmission of a portion of a packet. 
     
     
       13. The method of  claim 12 , wherein the portion of the packet is a continuous wave tone. 
     
     
       14. The method of  claim 12 , wherein certain ones of the plurality of possible antenna pairs include two antennas that are collocated. 
     
     
       15. The method of  claim 1 , further comprising:
 transmitting a plurality of packets to the portable access device; 
 measuring time-of-flight values for the plurality of packets based on response signals received from the portable access device, wherein the response signals are transmitted based on the plurality of packets; 
 based on the time-of-flight values, determining whether another device is performing a range extender type relay station attack; and 
 preventing access to an interior of the vehicle in response to detecting the range extender type relay station attack. 
 
     
     
       16. The method of  claim 15 , wherein the portable access device is a key fob or a cellar phone. 
     
     
       17. The method of  claim 1 , further comprising encrypting an identifier of the best antenna pair,
 wherein the transmission of the one or more additional packets includes the encrypted identifier of the best antenna pair. 
 
     
     
       18. The method of  claim 1 , wherein during the iteratively performing of the algorithm:
 the selected frequency is selected to be tested; and 
 the selected antenna pair is selected to be tested. 
 
     
     
       19. The method of  claim 1 , wherein during the iteratively performing of the algorithm the first RSSI and the response signal from the portable access device are received via the selected antenna pair. 
     
     
       20. The method of  claim 1 , wherein each iteration of the algorithm includes a different selected frequency to test and a different antenna pair combination not previously selected during a current execution of the algorithm such that at least one antenna of the different antenna pair combination was not previously tested during the current execution of the algorithm. 
     
     
       21. The method of  claim 1 , wherein:
 each iteration of the algorithm includes a different antenna pair combination not previously selected during a current execution of the algorithm such that at least one antenna of the different antenna pair combination was not previously tested during the current execution of the algorithm; and 
 at least one of the selected antenna pair combinations is tested for more than one selected frequency. 
 
     
     
       22. The method of  claim 1 , wherein the best antenna pair and the one of the plurality of frequencies are selected, such that the selected frequency and antenna pair combination has the highest RSSI values out of the first RSSIs and the second RSSIs. 
     
     
       23. A vehicle system for communicating with a portable access device, the vehicle system comprising:
 a plurality of antennas with different polarized axes; and 
 an access module iteratively performs an algorithm, wherein the algorithm includes a series of operations comprising
 selecting a frequency from a plurality of frequencies, 
 selecting an antenna pair from the plurality of antennas with different polarized axes, 
 transmitting a packet from a vehicle to the portable access device via the selected antenna pair, 
 receiving a first received signal strength indicator (RSSI) and a response signal from the portable access device, wherein the first RSSI corresponds to the transmission of the packet, and 
 measuring a second RSSI of the response signal, 
 
 wherein the access module
 obtains the first RSSIs and the second RSSIs measured during iterative performance of the algorithm; 
 based on the first RSSls and the second RSSIs, selects (i) a best antenna pair of the plurality of antenna with highest RSSI values out of the first RSSIs and the second RSSIs, and (ii) one of the plurality of frequencies, to provide a selected frequency and antenna pair combination; and 
 transmits one or more additional packets using the the selected frequency and antenna pair combination. 
 
 
     
     
       24. The vehicle system of  claim 23 , wherein the access module:
 measures time-of-flight of the one or more additional packets including time to transmit the one or more additional packets to the portable access device and time to receive one or more responses from the portable access device; and 
 based on the measured time-of-flight, estimates a distance between the vehicle and the portable access device. 
 
     
     
       25. The vehicle system of  claim 24 , wherein the access module detects whether a device is attempting to perform a range extender type relay station attack based upon the estimated distance. 
     
     
       26. The vehicle system of  claim 24 , wherein the access module, if the portable access device is attempting to perform a range extender type relay station attack, performs a countermeasure including preventing access to the interior of the vehicle. 
     
     
       27. The vehicle system of  claim 26 , wherein the countermeasure includes notifying an owner of the vehicle of the range extender type relay station attack. 
     
     
       28. The vehicle system of  claim 23 , wherein the access module:
 exchanges multiple pairs of unmodulated carrier tones with the portable access device at multiple frequencies, wherein the unmodulated carrier tones include received tones and transmitted tones; 
 measures the phases of the received tones relative to the transmitted tones; 
 gathers the measured phases and frequency data; and 
 estimates distance between the vehicle and the portable access device using the measured phases and the frequency data. 
 
     
     
       29. The vehicle system of  claim 28 , wherein the access module detects whether the portable access device is attempting to perform a range extender type relay station attack based upon the estimated distance. 
     
     
       30. The vehicle system of  claim 23 , wherein the portable access device is a key fob or a cellar phone. 
     
     
       31. The vehicle system of  claim 30 , wherein:
 the portable access device encrypts an identifier of the best antenna pair; and 
 the transmission of the one or more additional packets includes the encrypted identifier of the best antenna pair.